The present invention relates to multilayer packaging films useful for producing aseptic packages. More particularly, the present invention relates to multilayer films and methods for producing aseptic stick-pack packages. Machines for packaging food products are known in which packages are formed from a continuous tube of packaging material defined by a longitudinally sealed portion. The choice of packaging material depends on the product to be packaged, but in most applications, the packaging material incorporates more than one material in the structure that is assembled by lamination or coextrusion processes.
Aseptic packaging applications require that the packaging film provide several basic requirements for success in the marketplace. First, the packaging film must be suitable for use in contact with the intended product such as a foodstuff or medicinal product as required by the U.S. Food and Drug Administration, and must comply with applicable material migration requirements such as for hexane extractables. Second, the packaging film must provide physical integrity to assure containment of the product and maintenance of the sterility, as well as the ability to be processed in packaging machines. The term physical integrity applies to the structural integrity of the packaging film itself, as well as that of any closures and seals, formed therein or applied thereto, to assure package soundness and hermeticity during package formation, handling and distribution. Third, the packaging film must be able to be sterilized and be compatible with the method of sterilization used (i.e., heat, chemical, or radiation). And lastly, the packaging film must provide adequate barrier protection to maintain product quality until it is used. Barrier protection means control over the transmission of oxygen, moisture, light, and aroma through the package as required by the intended product.
In typical processes for producing aseptic packages the packaging film is unwound off a reel and fed through a sterilizing unit in which it is sterilized, for example, by immersion in a bath of liquid sterilizing agent such as a concentrated solution of hydrogen peroxide and water to destroy putrefactive microorganisms.
More specifically, the sterilizing unit may comprise a bath filled, in use, with the sterilizing agent in which the strip is fed continuously. The bath may conveniently comprise a reservoir of hydrogen peroxide solution wherein two parallel vertical branches connected at the bottom to define a U-shaped path of film having a length depending on the traveling speed of the film and such as to allow enough time to treat the packaging film. For effective and fairly fast treatment, so as to reduce the size of the sterilizing chamber, the sterilizing agent is usually maintained at a high temperature of, say, approximately 70° C.
The sterilizing unit may comprise an aseptic chamber in which the packaging film issuing from the sterilizing bath is subjected to mechanical processing (e.g. by drying rollers) and thermal/fluidic processing (e.g. by hot-air jets) to remove any residual sterilizing agent. The amount of residual sterilizing agent allowed in the packaged product, in fact, is governed by strict standards (the maximum permissible amount being in the order of a few parts per million).
Generally, before leaving the aseptic chamber, the film is folded into a cylinder and sealed longitudinally to form, in known manner, a continuous, vertical, longitudinally sealed tube. More specifically, the packaging film is fed vertically through a number of successive forming assemblies, which interact with the film to gradually form the film from a generally flat sheet, through an open C-shape to a substantially circular shape. The tube of packaging film is filled with the product and then fed to a forming and (transverse) sealing unit for forming individual packages and by which the tube is gripped between pairs of jaws to seal the tube transversely and form aseptic packages. Cutting the sealed portions between the packages then separates the pillow-shaped packs.
Packaging machines of the above type are used in a wide range of food industries; and performance of the packaging film, in particular, is such as to amply conform to standards governing asepticity of the packages and residual sterilizing agent.